This invention relates to the manufacture of improved compositions of the type comprising flake-shaped additives dispersed in binders, usually organic resin and polymer binders, to achieve a flake-related advantage such as an improvement in electroconductivity.
The prior art has generally recognized the fact that conductivity is best imparted to organic resin compositions by utilizing flake forms of conductor particles in the composition. Moreover, there have been a number of procedures discovered for improving the efficiency of conductive flake--usually silver flake--in the compositions. Some such work has described the use of limited amounts of non-flake, non-conductive, powders to minimize the flake particles from lining up in parallel relationship one to the other. Such parallel relationship is known to limit the probability of adjacent flakes making the desired contact. Silica particles have been used for such a purpose.
Also, another type of silica particles, the ultra-fine pyrogenic silica sold under the trademark Cab-O-Sil by Cabot Corporation has, been utilized in a great number of materials from calamine lotion to conductive, resin-based liquid systems to retard the settling of suspended solids. This silica material, also non-conductive, works in a number of ways, depending upon the particular system, but in general works to thicken the liquid phase through hydrogen bonding or some other such mechanism. The objective of such work was to overcome the detrimental tendency for metal flakes to settle out of lower viscosity systems such as solvent-based inks and paints. Settling results in non uniformity application and consequent erratic conductivity values.
In general, it has been desirable to provide such conductive compositions that are improved in terms of conductivity and settling characteristics and to do it without the necessity of adding non-conductive diluent particles to the composition.